1. Field of the Invention
The present invention relates to photoelectric conversion apparatuses, and particularly to photoelectric conversion apparatuses in which a plurality of photoelectric conversion elements (hereinafter referred to as photosensor elements) are arranged in an array.
The photoelectric conversion apparatuses according to the present invention are applied to, for example, color or monochrome image sensors or the like, used with image readers, digital reproduction devices, or the like.
2. Related Background Art
FIG. 1 is a schematic circuit diagram of a conventional monochrome line image sensor. In FIG. 1, photocurrents corresponding to the quantities of incident light on respective sensor elements S.sub.1 -Sn flow through the respective sensor elements and the quantities of electric charges corresponding to the respective photocurrents are stored as image signals in the corresponding capacitors C.sub.1 -Cn, and these image signals are output sequentially by a scanning circuit 4.
FIG. 2 illustrates a diagrammatic structure of the conventional line sensor. In FIG. 2, photosensitive elements S.sub.1 -Sn, each including a photoconductive film of CdS, CdS/Se or the like, are formed in a line on a long substrate 1 of glass or the like. Terminals on one side of the photosensitive elements are connected to a common electrode 2 and the other-side terminals on the other side of the elements are connected via individual electrodes to corresponding parallel input terminals of the scanning circuit 4. Portions of the respective electrodes and an opposite grounding electrode 3 hold an insulation layer therebetween to form capacitors C.sub.1 -Cn.
The number of photosensitive elements S.sub.1 -Sn required is 3,360 or more if, for example, an A4 sized (210 mm) document is to be read. This is because a reading resolution of more than 16 dots/mm is desirable if human eyesight characteristics are considered.
Recently, with the spread of personal computers and color printers, the demand for an image reader which can read color has increased. It is, however, very difficult to attain a compact color image reader using the conventional line image sensor.
First, in order to read color, one pixel must be constituted by three different-color (red, green, blue; hereinafter referred to as R, G, B) photosensitive elements. Thus, when the color of, for example, an A4-sized document is read, the number of photosensor elements required is 3,360.times.3=10,080. If all of these elements are arranged in lines, as shown in FIG. 2, the wiring pitches at the junctions of scanning circuit 4 will each be 20.8 .mu.m, so that it is impossible to use wire bonding or heat seal junction techniques.
It is very difficult to form, with high stability and yield, such microwiring and microcircuits arranged on the same long substrate 1 using thin film techniques.
In order to solve such problem, matrix wiring used in area image sensors, etc., has been employed.
FIG. 3 is a schematic circuit diagram of a conventional color line image sensor using matrix wiring.
In the same Figure, light enters from a document into photosensor elements Sr.sub.1 -Srn (hereinafter referred to as Sr), Sg.sub.1 -Sgn (hereinafter referred to as Sg), and Sb.sub.1 -Sbn (hereinafter referred to as Sb) through corresponding R, G and B color filters. If a high-level potential is applied to a terminal Tr, and the scanning circuit 4 is driven in the meantime, the output signals of photosensor elements Sr, i.e. signals representative of red components in a line in the document are sequentially output. Subsequently, in similar ways, the respective output signals of sensors Sg and Sb, i.e. signals representative of green and blue components in the same line are sequentially output.
Employment of such matrix wiring serves to reduce the number of output signal lines of the photosensor elements compared with employment of the circuit structure of FIG. 1. However, since the number of photosensor elements increases to three times that of photosensor elements of the monochrome type and each photosensor element requires a switching transistor, a very fine microworking technique is required to form the matrix circuit shown in FIG. 3. In addition, the manufacturing process is complicated and alignment of photosensor elements requires high precision because formation of three wiring patterns, one for the photosensor elements for each color and because of formation of a lamination of these patterns are required. Thus according to this conventional method, a miniaturized low-cost color line image sensor cannot be obtained.
Such a problem does not only occur in color line image sensors. A similar problem will of course occur in color area image sensors as well as in those monochrome type area image sensors which each include a multiplicity of photosensitive elements for high resolution purposes.